Patent GB-816142-A (GB)
Title: Improvements in fluid pressure motors
Inventor: NICHOLS ELTON FINDLAY
IPC: B60S1/10
Filed: 1955-09-01
Abstract: 816,142. Compressed-air and vacuum engines. SPRAGUE DEVICES Inc. Sept. 1, 1955, No. 25157/55. Classes 122 (2) and 122 (3). A fluid-pressure motor for driving a windscreen wiper comprises a piston 50 reciprocating in a cylinder 13 by the action of fluid supplied alternately to opposite ends of the cylinder under the control of a spool valve 72 which is provided with circumferential seals 74, 76, 78, 80 on its four lands and reciprocates in a cylinder 16 so that these lands control the passage of fluid through an inlet port 84, outlet ports 94, 95 and a pair of passages 88, 89 communicating with opposite ends of the cylinder 13, the movement of the valve between its two positions being caused by fluid passing from an intermediate portion of the cylinder 13 to an end portion of the cylinder 16 through ports 98, 99 when these are uncovered by the piston 50. The cylinders 13, 16 are arranged in parallel relation in a housing 10 closed by end plates 22 and provided with a removable closure 44. The piston 50 consists of a longitudinal member 56 of U cross-section having a circumferentially-sealed piston at each end, and a rack 58 formed on the member 56 engages a gear sector 62 on a transverse shaft 30 carrying the mounting arm of the windscreen wiper. The valve 72 comprises four circumferentially-sealed spools on a shaft 70 movable longitudinally in the cylinder 16. This cylinder is provided with a central fluid inlet port 84, two outlet ports 94, 95 spaced equally on opposite sides of this port, ports 88, 89 respectively connected by passages 86, 87 with ports 92, 93 opening into the ends of the cylinder 13, and two ports 98, 99 disposed in the separating wall 96 between the cylinders 13, 16. The ports are so disposed in relation to the four spools that, with the latter in the right-hand position shown, fluid passes from the port 84 through the port 89, passage 87 and port 93 to the right-hand end of the cylinder 13 and is withdrawn from the other end through the port 92, passage 86 and ports 88, 94. The resultant leftward movement of the piston continues until the uncovering of the port 99 permits fluid to pass from the right-hand end of the cylinder 13 to the corresponding end of the cylinder 16 and so moves the valve to its opposite limit position ; ' the fluid flow to the cylinder 13 is thereby reversed and the piston 50 is returned until the uncovering of the port 98 again reverses the position of the valve. If desired, the port 84 may be open to atmosphere and the ports 94, 95 connected to suction, or suction may be applied to the port 84 and the ports 94, 95 open to atmosphere, in which case some rearrangement of the ports 88, 89 and passages 86, 87 is necessary (Fig. 5, not shown). When using suction, the space between the two sealed ends of the piston must be maintained at sub-atmosphere pressure to prevent the passage of air at atmosphere pressure from that space through the ports 98, 99; this may be achieved by providing an airtight seal at the closure 44 and evacuating air from the piston space after assembly of the device, or connecting the piston space with the suction line, or providing a port in the separating wall 96 between the cylinders 13, 16 in such a position that it remains in communication with the suction line whatever the position of the valve.